


Ba-da-bing Ba-da-bum

by Mikachi_Chan



Category: One Piece
Genre: Fluff, Heart Swap, M/M
Language: English
Status: Completed
Published: 2020-01-01
Updated: 2020-01-05
Packaged: 2021-02-27 13:33:38
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 4
Words: 3,786
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22067830
Author URL: https://archiveofourown.org/users/Mikachi_Chan/pseuds/Mikachi_Chan
Summary: His life, in my hands. And he shows not a drop of fear but instead, faith, Law thought to himself.In which Law is astonished by Luffy's open trust in him.
Relationships: Monkey D. Luffy/Trafalgar D. Water Law
Comments: 18
Kudos: 250





	1. Dr. Heartswapper

**Author's Note:**

> This is my 1st Lawlu fanfic, and the first serious fanfic I have ever written. I'm going to be posting this on Jan 1, 2020 to mark a new decade. I never thought I was ever going to contribute to a fandom like this. I'd cross my fingers for luck, but that's the equivalent of a Vietnamese middle finger.

“Torao!!” called Luffy, slingshotting himself to the other side of the Thousand Sunny, up to the port bow’s railing. He wrapped his rubbery limbs around a busy looking Law who was reading a journal. “At Punk Hazard, I remember hearing you did a switch a roo thingy with Smokey and that bird woman’s hearts.”

“Yes, I did,” answered Law with a slightly annoyed face. He had plenty to learn about diseases and injuries in the New World from the medical journal in his hands, not the time to entertain this hyperactive monkey he made an alliance with. “Let go Straw-hat ya.”

“WOAH! You can remove hearts, just like that? And Smoky was still alive. That’s so cool Torao!,” Luffy’s face beamed. A thought crossed his rubbery brain. “Take mine out. I want to see it.”

Law raised an eyebrow. “That’s awfully trusting of you Straw-hat ya. What if I were to crush it right in front of your eyes?” The corner of his mouth tipped up into a smirk. 

Without a hint of hesitation, Luffy responded with a smile, “Torao wouldn’t do that.”

Law’s eyes grew a little wider in bafflement and a bit in disbelief. His smug look wiped clean. How could anyone be so naive, be so open? They were pirates for pirates’ sake. Law said he wasn’t going to betray Luffy back on Punk Hazard, but he figured that any other pirate looking to stab another in the back would do the same. He blinked. “Suit yourself.”

Luffy got off of Law and stood in a confident stance, hands holding his shirt open for easier access, chest forward, chin up with a continued smile. Law placed the medical journal down and stood up, forming a small Room to surround the both of them. Law pulled back his arm as Luffy held his shirt apart to make it easier to access his heart. 

“Scalpel,” Law said the name of the move. He placed his hand on the X shaped scar on Luffy’s chest and pulled out a clear cube with a pink beating heart in it. He held it up to eye level to see. It beat once, twice. His life, in my hands. And he shows not a drop of fear but instead, faith, Law thought to himself. Then he gave it to Luffy who had his hands eagerly out, waiting. 

“Woah! This is so cool!” Luffy awed at his own beating heart. “Baa-dum baa-dum baa-dum.” He mimicked its paced. 

“Be careful with it Straw-hat ya. Don’t want to accidentally commit suicide before becoming Pirate King do you?” Law warned. “Just because your heart is out of your chest doesn’t mean you are invincible if you hide it away. In fact, it may make you even more vulnerable.”

“Hey, I got an idea!” Luffy exclaimed. 

“I’m sure it’s a bad one.”

“What if we switch hearts? What would happen? Let’s try it Torao!” Luffy’s face shined bright at what a cool idea it was to feel someone else’s heart in his chest. 

“No,” Law bluntly rejected him. “It’s a stupid idea. What if we get attacked? We can’t risk that.”

“But Toraoooo,” Luffy whined. “It’ll be fun! Just for a little bit. Nothing will happen in such a short time. You’ll be perfectly safe, I promise.” Luffy stared up at him with big, wide eyes full of life. As much as Law would hate to think so, Luffy eased his nerves just a bit. 

Law thought for a moment. He had never physically switched anybody’s heart with another. Only switched the minds of his enemies, which disadvantaged his enemies and entertained him at the same time. The hearts removed through the Ope-Ope Fruit continued acting like a regular heart would outside of a chest cavity. Would the hearts swapped still be connected to the original, or adapt to the new chest like an organ transplant? Maybe it was a mix of both? It was an interesting question and Law was very curious about the results. 

“C’mon Toraooooo,” Luffy persisted. “Do it! I know you want to know as well!”

Law hesitated for a moment before saying yes. “Be very very careful Straw-hat ya. If anything happens I will kill you on the spot, do you hear me?”

“Wooo Torao!! Let’s do this!” Luffy jumped in excitement, careful to not drop his heart. 

“Room.” Law pulled out his heart and slid it into the square-shaped hole in Luffy’s chest. Luffy held out his own heart for Law to take and put into his chest.

Luffy’s heart beating in his own chest showed three things. That the Ope-Ope Fruit kept separated hearts in different bodies as separate - no working with a new body, the skin over the heart went along for the ride, and that it was a calming experience to feel the heartbeat of another person. 

“Waahh Torao! Your heartbeat, it’s very different. Ba-dum ba-dum ba-dum,” Luffy commented in wonder. 

“How come my heart gets one ‘ah’ instead of two?” Law joshed. “Is my heartbeat faster than yours?”

Luffy laughed. “Yeap! That’s weird Torao. My heart should go faster cause I’m running around all the time. Yours should be slower cause you just stand there.”

Law, with his medical knowledge of hearts, said, “No. More active people have slower heartbeats. I’m not as active as you, considering I don’t run in circles all day. Can’t you ever calm down and stay still, or do you always have to be so lively?” The doctor’s mouth upturned just a bit.

“No way! Being still is boring! Running around gets you to many places that are a lot more fun than your current position,” Luffy stated. “Like Sanji’s kitchen where meat is!” Then, he turned, jumped off the helm deck to the grass meadow, and ran into the kitchen. 

Must have gotten hungry Straw-hat ya, Law thought to himself. Wait. He felt the beating in his chest get faster as Luffy ran off. It slowed down after a couple more seconds. Then sped up with adrenaline running throughout the bloodstream. Luffy had his heart. And Sanji was chasing after him, evident by the angry screaming cutting through the air from where Luffy ran off to, threatening to ‘chop up that gummy ass and turn it into dessert’. 

Law turned to join in the chase to get his heart back, but paused in his steps. This feeling of a lively beating heart was a new sensation. Rarely did he ever feel this way. The only times his heart sped up was during fights and moments of high stress. A quick heartbeat was often associated with skirmishes and conflict. But this was different. There was no hostilities around to make the rhythm in his chest. Instead it was a merry tune. Law wasn’t complaining about it, so he went back to what he was doing, listening to the ba-dum ba-dum ba-dum of Luffy’s heart in the background.


	2. Dr. Heart All Mushy

Throughout the day, the heart in Law’s chest changed rhythm many times. At dinner time, the heart was faster as it tried to pump more blood to Luffy’s attempts at stealing food from the plates of everyone around him. After dinner, there was a game of charades. Nothing much happened to the heart, except when Luffy laughed. And Luffy laughed a lot. It felt like it was jumping with joy at Franky’s current attempt to communicate through interpretive dance. At this point, Law wondered whether or not Luffy had forgotten about the heart switch.

The moon rose into the starry night sky and the Straw-hats began getting ready for bed. Law called out to Luffy as he walked to the men’s dormitory. “Straw-hat ya, come here.”

“Hmm Torao?” Luffy turned around and walked to the foremast’s bench where Law had been sleeping at the past few days.

“Do you remember that you have my heart? I want it back,” Law said. 

“Ah! But your heart is so nice to listen to Torao,” Luffy protested.

Yours as well Straw-hat ya, Law responded in his head. “Well I would like to sleep knowing that I have my heart where it belongs.” Law made a Room surrounding the two of them. 

Luffy puffed out his cheeks and crossed his arms. “Hurry up Straw-hat ya.” 

“If I sleep out here with you, you would sleep knowing where your heart is,” Luffy thought out loud. He uncrossed his arms and yanked the front of Law’s shirt to bring attention to his brilliant idea. “And I would still be able to listen to it. I’m a genius Torao!”

Law was too tired to fight Luffy at this hour for his heart. He’ll get it back in the morning. “Fine.” Law dispelled the Room and turned to sit on the foremast’s bench, crossing his arms. Luffy plopped himself right next to Law and reached an arm over to pull him closer. 

“An outdoor sleepover Torao! This is going to be fun,” Luffy laughed. Law closed his eyes hoping the sweet embrace of sleep were to descend upon him soon. 

Luffy shifted to a horizontal position, using Law’s lap as a pillow. Law didn’t mind, but he was jealous of the fact that Luffy could just fall asleep that fast. Sleep decided to come to the other captain first, leaving Law listening to the ambient noise around him. The ship rocked like a gentle cradle, a small wind stroked his hair, tiny snores set in a steady rise and fall, the heart in his chest beat nice and slowly, a lullaby singing him to sleep. Law felt his consciousness slip in and out, fading gradually into slumber. 

Sanji and Brook were the first ones to notice near the end of the nightly watch. The rising sun rays basked the ship’s deck in a warm glow over the cuddling captains. Sanji glanced at the couple with a small smile. “I would smile at a wholesome scene as well Sanji-san, but I don’t have a face to do so!” laughed Brook as he walked with Sanji to the kitchen for a cup of morning tea. 

Robin was next, walking to the library with a knowing smile that her captain was making progress in a promising alliance. 

Nami and Chopper awed at the cold, creepy doctor who was being used as a pillow for their warm, cheery captain. They wondered how Law ever got to where he is right now. Zoro only spared them a passing glance, at the top of the crow’s nest. 

Usopp snickered at the couple when he woke and walked out onto Sunny’s deck. He fetched a den-den mushi to take pictures of this precious moment. Nami was going to be grateful for these. 

Franky did his super pose when he walked by Law and Luffy sleeping together. “OW! Super cool those two getting together!” he whisper yelled, careful not to wake them up. 

Some time later, Luffy awoke to see above him, the sleeping, serene face of Law. Law’s heart sang an evenly calm pace. Luffy stared at his face for awhile, until Law began to stir. His eyes opened. “Good morning Torao!” Luffy beamed at him a smile that rivaled the sun. 

Law smiled a faint smile. He had a pleasant sleep, with barely any dreams to disturb him. That put him in a better than average mood. “Morning to you too Straw-hat ya.”

“I’m hungry,” Luffy stated. He got up from Law’s lap and stretched his limbs towards the sun. To Law, Luffy paralleled a sunflower growing out of the grassy meadow of the Sunny. The sun ever shining and nourishing to the beautiful earth below. Wait, what was Law thinking? The doctor who was supposed to not be a sentimental sap, shook his brain. The effects of hunger and a bit of drowsiness were showing.

He got up and calmly followed Luffy running across the grass to the delicious smell of breakfast coming from the kitchen. The beat in his chest speeding up, reminding Law where his heart was. They were going to have to switch back. Just after breakfast.

**Notes for the Chapter:**

> Should i have put this with the last chapter? This feels like a nice break in the story for the progression of time, so Im going to keep it separate.


	3. Dr. Heart Full of Embarrassment

**Summary for the Chapter:**

> Straw hat's version of shovel talk.

Law was the last one on the ship to arrive at the dining hall, excluding Caesar who didn’t get to dine with them. The table had 8 seats perfect for the main crew who didn’t cook. There was a sofa to the right, which was occupied by Nami and Robin, lively talking away with an open book between them. This left 2 empty seats at the main table. Luffy was at the head of the table as usual, stealing food from the others. Zoro and Brook were on one side, talking about sword techniques. Franky, Chopper, and Usopp on the other. Law took the seat next to Brook at the other end of the table. The farther you were from Luffy, the more time you had to defend your meal, even if it was just milliseconds. Weirdly, Law trusted Luffy with his heart, but not with his food. 

“Ah, good morning Law-san,” the polite voice of Brook greeted him. Law turned to his right to see a smiling skeleton. How did he know Brook was smiling if he had no face to show was beyond him. “I hope you slept well last night.”

A faint blush appeared on Law’s cheeks. “Yes, I did sleep well, thanks.” 

“I sleep as soundly as the dead, because I am one!” Brook laughed at his own skull joke. Law turned his attention to stab the rubbery hand who was trying to steal his chunk of fried fish. He missed, but so did Luffy. 

“So Torao, how’d you get with the captain?” Sanji approached the table and sat the empty seat beside him. His nonchalant face looked at Law directly in the eye. 

Law’s face could only convey a fraction of how horrified he was to hear Sanji implying that him and Luffy were dating. “We’re not dating! This is just an alliance, nothing more.”

“Oh?” Sanji’s curly eyebrow rose along with his tone. “That back there seemed a lot more than ‘just an alliance.’ Was captain bothering you?”

“He wasn’t.” Law recomposed himself and straighten up. He was not about to explain how and why Luffy and him decided to switch hearts and sleeping positions last night. Not ever. He was glad his shirt covered his chest, otherwise it would be a dead giveaway. Luffy on the other hand, proudly showed his torso to the world. The darker patch of skin and parts of his tattoos clear as day against olive skin and pink scar tissue. Sanji followed Law’s glance to the head of the table. His eyes landed on the lively food thief and the oddity on his chest.

“Care to explain that Surgeon of Death?” he pointed to Luffy’s chest. “If you harmed him in any way, you already know what will happen.”

“Rest assured I won’t be bringing harm Straw-hat ya,” Law started. He stopped. Did he really have to tell Sanji what happened? Telling him would put a damper on his reputation as a feared, cruel, merciless pirate who could easily save or rid of a life. Curse him for being so careful in protecting his captain. Curse Luffy for being so open about everything. Curse himself for agreeing to Luffy’s demands. 

Sanji began to tap his feet, finger resting on the table, twitching. He was getting impatient of Law’s unusually flustered attitude. Why was he acting like this? “Oi! Luffy! What’s that dark patch over the area on the heart?” 

Law seized up. There goes his reputation down the drain. Luffy was not one to quickly read the room and decide on what to do. He was done for. 

Luffy turned to Law and Sanji. He looked down at his chest. “Oh this? It’s Torao’s heart.”

“Huh? Where’s yours, then?” Sanji’s interest piqued. 

“With Torao! We switched hearts.”

Sanji’s fidgeting stopped and he took a moment to process this information. He slowly turned to Law with a cheeky smile. “The infamous Surgeon of Death who can amputate his enemies - without much care or effort - to leave them for dead, who can work surgical miracles, is a romantic sap. Who would have guessed?”

Law pulled down the rim of his hat to hide the embarrassed blush creeping up on his face. Sanji began to chuckle. Chuckle turning into a full on laugh. Laugh crescendoing to a near roar. He began to bang on the table and slapped a hand onto Law’s back. “That’s Luffy for you! You’ve become another victim to his charm. Next thing you know, you have married the future pirate king!”

Law wanted nothing but to hide in this current moment. And to get his heart back. “I can promise you, I will do no such thing. We remain allies.” 

“‘Allies’,” Sanji made air quoted with his hands. “More like a relationship- ” he laughed some more- “Don’t worry, I fully support this union between you and Luffy. Just know he’s a bit of a handful sometimes, maybe all the time.”

Law stayed silent as he glared daggers in the laughing cook. “I’ll keep that in mind Black Leg-ya,” he said through tight lips. 

While Law’s embarrassing moment went down, the rest of the Straw-Hats were listening to the entire thing, but they felt no need to torture Dr. Heartstealer, or rather Dr. Heartswapper, any further. He was their guest after all. Though this didn’t mean they weren’t going to comment about it in private.

Robin turned back to Nami on the couch with a small smile. “Seems Torao-kun affections for Luffy is being endorsed by Sanji.”

“Honestly, I still can’t wrap my head around the fact that Torao likes our idiot captain! They’re like complete opposites,” Nami said in disbelief. 

“They say opposites do attract,” Robin added.

“Hey hey, Chopper, Franky, wanna see some pictures of Luffy with his new boyfriend I snapped earlier this morning?” Usopp whispered to the group, pulling them closer so Law wouldn’t hear them.

“Ehhhh!! You have pictures?” Chopper squealed. He quickly covered his mouth, hoping Law hadn’t overheard. He looked over to the other end of the table and relaxed. Law was too busy wishing he was somewhere else, trying to hide his face from Sanji’s continued laughter. Nami, on the other hand, had heard Chopper loud and clear. She rushed over to the group.

“Pictures?! Show me!” Her eyes sparkled with Berri signs. It was obvious she was going to use it as blackmail against Law when the time came up.

“That’s super,” Franky congratulated Usopp. “Hurry up and show us them.”

“Yes, yes,” Usopp said as he discreetly pulled out 5 photos, all snapped in succession. The innocent moment of Luffy sleeping on top of Law was permanently captured. That was, until Law decides to slice them all in half if he found out. The pictures were relatively the same, just the snot bubble could be seen to increase in size when compared together. They were adorable. 

Nami took one of the photos, folded it up into her pocket for safe keeping. She patted Usopp on the back and beamed.“Good job Usopp!” 

The usual chaotic breakfast was enhanced with an air of giddiness, the new alliance was going good. Their new friend was welcomed with open arms.

**Notes for the Chapter:**

> If there are any mistakes in my writing, please let me know. If you got any comments, please do share them.
> 
> I drew that picture Usopp took of them. A lacking picture really, but I tried.   
> Can be found here: https://how-is-thy-day.tumblr.com/post/190052065430/i-drew-this-first-time-trying-out-digital-art#  
> since i don't know how to put pictures on AO3. If you know, please tell me how.


	4. Dr. Heart Full of Hope

Law kept to himself for a while at the stern of the Sunny after breakfast, healing his wounded ego. The waves below pulled from the advancing sea lion’s path. The roar of the sea providing white noise. Of all the things he would have expected to do in life, never had ‘get laughed at for switching hearts with an idiot who he was in an alliance with and get dating advice for said idiot’ ever crossed his mind. He sighed. Plans on how to go about this situation failed to come to light. 

His sulking came to an end when Luffy landed just meters away from a good swing around the Sunny. “I’ve found you! So this is where you’ve been,” Luffy jumped with joy, smile cutting through the foggy thoughts.

“What Straw-Hat ya? Have you come to return my heart? I would like it back soon enough,” Law started. “We are going to arrive at Dressrosa in a few days. I’m sure your rubber attacks would stretch out my heart to the point of popping.”

“Hmmmmm. Hmmmmmm.” Luffy squinted his eyes, tilting his head to think. A moment passed. And another. 

Then he snapped his head back and eyes opened in a realization. “Ah! Gear 2nd. That’s when I increase the flow of nutrients to make me go faster. I’m able to do it due to the Gomu-Gomu Fruit. But you don’t have it. That’s a problem! I don’t want you to die Torao.”

I don’t want you to die Torao. Those words rang clear in Law’s ears. The heart in his chest keeping a steady melody against the skipping of his own. It had been a while since he felt that statement for himself. A while since someone had expressed that statement for him.

The memory of Cora-san’s multiple failed attempts of curing amber lead disease through incompetent doctors and his final mission to get the Ope-Ope Fruit resurfaced in his mind. Cora-san had wanted him to live and made damn sure he did, sacrificing his own life to do so. The stupidly smiling face that he made to the dying child stowed away in a treasure chest of gold had been his final farewell.

Law forced himself into the present, in front of the grinning young man in a straw hat. “Thank goodness. Let’s switch back,” Law got up from his position in the cool shade and walked out into the mellow sunlight. 

Luffy gave a tiny whine, but complied. He was going to miss the rhythm in his chest. It was different from his. Sometimes it jumped when Law was feeling disoriented with the Strawhats, unlike his own. He was never in such situations, he walked confidently into everything. The past day, Luffy got to experience what he had never felt before.

“Room,” he quickly switched the hearts with a Shambles. Law was at ease, the familiar beat greeted him as it settled back into the cushion of the surrounding lungs. The pleasant guest returned home across from him. 

Luffy looked down and placed his hand over his heart. He looked up and smiled. “Let’s do it again after we kick Mingo’s ass.”

Law looked to the side, thinking. “We’ll see Straw-Hat ya.” A faint smile appeared on his face. The other captain spoke of taking down such a powerful man so casually, so full of conviction. A spark of hope ignited itself within. Cora-san was going to be avenged for sure.

**Notes for the Chapter:**

> I wrote this entire fic for my English hw lol.   
> I feel this is a very short chapter. Maybe it should have been longer? important stuff happened in such a short time, feels like I'm kinda undercutting it all with the length. Ah well, my break is ending tomorrow, and I'm not going to have as much time to goof around and write stories so i might as well finish this today.
> 
> Thank you for all that have read this :D  
> I'm greatly flattered that anyone would like this short piece. If I could bow in thanks, I would.

**Author's Note:**

> I was planning to post the entirety of this fic, but unfortunately I can't finish in time. It surprised me how long this was going to be. I thought the story would be short, but that's writing I guess.


End file.
